The emotional debate over free speech versus free political spending, which erupted onto the Senate floor this week, exposes a deep rift on Capitol Hill and at the nation’s leading civil rights group, the American Civil Liberties Union.

“There is a very, very significant divide within the ACLU on this,” said New York University law professor Burt Neuborne, one of six prominent former ACLU officials who wrote to members of the Senate Judiciary Committee on Sept. 4 to publicly denounce the national ACLU’s campaign finance position. The letter was released as the Senate prepared to take up a resolution authored by New Mexico Democrat Tom Udall to amend the Constitution to permit political spending limits, something the Supreme Court has ruled violates the First Amendment.

“While, as present and former leaders at the ACLU, we take no position in this letter on whether a constitutional amendment is the most appropriate way to pursue campaign finance reform, we believe that the current leadership of the national ACLU has endorsed a deeply contested and incorrect reading of the First Amendment as a rigid deregulatory straitjacket that threatens the integrity of American democracy,” read the letter, which was signed by Neuborne, the ACLU’s former national legal director, and by its former executive director, Aryeh Neier, and its onetime general counsel, Norman Dorsen, among others.

In an interview with CQ Roll Call, Neuborne said he spearheaded the letter in response both to a June ACLU letter to the Judiciary panel strongly opposing a constitutional amendment, and to conservative leaders’ tendency to invoke the ACLU in denouncing the amendment. Sen. Ted Cruz, R-Texas, has frequently referenced the ACLU letter, which warned: “Tinkering with the First Amendment in this way opens the door to vague and over-broad laws, which both fail to address the problem that Congress wishes to solve and invariably pull in vast amounts of protected speech."

Laura Murphy, director of the ACLU Washington legislative office, who co-signed the June letter that Cruz often cites, acknowledged the division within her organization. But she rejected what she called "hyperbolic rhetoric" from Neuborne and former ACLU leaders. She noted the ACLU board, which has consistently challenged campaign finance limits on First Amendment grounds over four decades, amended its position in 2010 to endorse limits on campaign contributions, which the group had previously opposed.

“I think that there is a deep divide within the ACLU about this issue,” Murphy told CQ Roll Call. “But we are taking positions that are supported by our national board. Our most recent policy that endorsed contribution limits for the first time also opposed a constitutional amendment. So which particular contested and incorrect reading of the First Amendment are they talking about? Are they upset because we do support contribution limits? Are they upset because we oppose a constitutional amendment?”

It’s not the first time former ACLU leaders have publicly clashed with the national ACLU over campaign financing. In 1998, Neuborne, Neier and seven other former ACLU executives publicly denounced the ACLU’s opposition to the McCain-Feingold soft money ban, arguing that “opponents of reform should no longer be permitted to hide behind an unjustified constitutional smokescreen.”

The Supreme Court’s 2010 ruling in Citizens United v. Federal Election Commission, which reversed longtime limits on independent political spending, has put the ACLU’s national leaders even more out of step with the organization’s rank and file, said Neuborne. “There is within the organization very, very significant discontent with the existing position.” Advocates of a constitutional amendment have released polls suggesting that voters support such an amendment on both sides of the aisle, and 16 states and 550 cities and municipalities have passed resolutions calling for an amendment.

The ACLU's sensitivity to opposition within its ranks may help explain why the organization took no position on the McCutcheon v. FEC ruling earlier this year that overturned aggregate contribution limits, which had placed an cap on overall donations to candidates, parties and political action committees in a single election cycle. Yet Neuborne said he and his colleagues — like the national ACLU — do not endorse the Udall resolution: “Most of us don’t think a constitutional amendment is the best way to go.”

Murphy stressed that the ACLU endorses campaign finance changes — but in the form of legislation that would match low-dollar contributions with public financing, as opposed to limits on spending. The ACLU opposes the leading congressional disclosure bill, the DISCLOSE Act, as over-broad — but endorses disclosure restrictions that are more narrowly tailored.

“I want to sit down and work with anybody who wants to have a practical and constitutional approach to reform,” Murphy said. “The ACLU is not saying ‘no’ to reform. The ACLU is saying ‘no’ to the constitutional amendment, and ‘no’ to the specific version of the DISCLOSE Act.”

Eliza Newlin Carney is a senior staff writer covering political money and election law for CQ Roll Call.Get breaking news alerts and more from Roll Call in your inbox or on your iPhone.